Electric arc extinguishing medium



ELECTRIC ARC EXTINGUISHING MEDIUM Filed Oct. 16, 1951 Nitrogen I-- Helium 0 l l l l I v V l 1 EMS, limp fni'erupzed if Niirogen 425-- R HeZium 51 0 E t l t i E l 20 4d 60 50 I00 /20 1 /0 150 I60 200 Gas zressure 55%; in

, used .is oil.

Patented Apr. 21, i936 UNITED STATES PATENT OFFICE William S. Edsall,

Condit Electrical chusetts Belmont, Mass., assignor to Manufacturing Corporation, Hyde Park, Mass., a corporation of Mass Application October 16, 1931, Serial No. 569,293 4 Claims. (Cl. 200-144) This invention relates to a novel medium for extinguishing an electric are such as is formed between the separable contacts of an electric switch or interrupter when it opens under load and when a fuse blows.

One of the main requirements of an are extinguishing medium is that it should extinguish the are rapidly so that the circuit positively is known to be interrupted within an instantfollowing the mechanical separation of the separable contacts or current carrying parts of the circuit interrupter, to permit switching operatlons to be carried out in closely-timed order, and to clear trouble from the circuit as quickly as possible. The rapid extinguishing of the arc is also highly desirable to avoid destruction of the arc-supporting members of the interrupter and the creation of high pressure of the extinguishing medium.

Further requirements of the extinguishing medium are that it should be inert with respect to the materials of the switch with which it is in contact, stable under the action of the arc, and with the air so that there is no danger of explosion or fire hazard. The are extinguishing medium also should be electrically insulating, so that it isolates the separated parts of the circuit, and should be capable of indefinitely repeated use.

Various liquid arc-extinguishing mediums have been proposed of which the one most universally Oil, however, is a complex chemical compound, is decomposed by the action of the arc into simpler hydrocarbons, one of which is carbon which can form a dangerous electrically conducting bridge between the interrupter'terminals, and others of which are fixed gases which can collect under dangerous pressure in the enclosing casing of the interrupter. .The oil and the vapors and gases thereof are combustible in air and have resulted in damaging explosions within the interrupter casings and fires externally thereoi;'.

Other insulating liquids, as carbon tetrachloride, have been used to some extent but in general are volatile at ordinary temperatures, decompose under the action of the arc and react chemically with the parts with which they are in contact.

' Electrolytes, as water, have been used to some extent but are conducting so as to require an especial design of the interrupter or the use of additional air or oil break switches in series with the terminals of the interrupter to provide positive assurance of potential isolation of the parts of the mechanically separated circuit. v

A gaseous arc extinguishing medium has certain advantages overa liquid medium. A gaseous medium, by reason of its lower density and viscosity, permits more rapid separation 01 the submerged interrupter contacts than a liquid medium; and the gaseous medium can move more quickly than a liquid into effective relation with the arc. While atmospheric air is commonly employed as the arc extinguishing medium in a certainclass of switches, it is unable to extinguish the circuit interrupting are rapidly and requires a long separation of the contact members of the switch for high voltages. Other gaseous mediums such as air under elevated pressure and carbon dioxide have been suggested, but without successful results.

I have conducted tests with various gaseous arc extinguishing media especially to determine their ability to rapidly extinguish circuit-interrupting power arcs and have discovered that helium, especially at an elevated pressure, can extinguish electric arcs much more rapidly than any other gas known to me that has been proposed for this purpose. Hence a novel arc extinguishing medium comprising helium constitutes an object 01' the present invention, because of its ability to satisfactorily contribute to or eifect the desired rapid extinguishment of the arc.

Fig. 1 illustrates curves showing the relation for various gases, between the number of cycles of alternating current arc duration, or rapidity of arc extinction, and, are current.

Fig. 2 are curves showing the eilect of pressure on rapidity of arc extinction.

Fig. 3 is a sectional view, more or less diagrammatically shown, of an electric switch adapted for use with the arc extinguishing medium embodying the present invention and,used to obtain the data for the curves of Figs. 1 and 2.

The switch herein shown comprises the pressure tight casing III having the removable cover 12, which carries the insulating bushings I having the exposed terminals 16 and the main current carrying, or brush, members l8 and areing members 20 within the casing. The switch includes a movableswitch member having a lifting rod 22 terminated in a bridging member 24 -which engages the brush members 18 and carries is closed, and the mechanically by a conductor 28 that is carried by the lifting rod and has looped portions 30 adjacent the arcing members 26 that provide magnetic blow-out fields in the arc zones and also maintain the pairs oi! arcing members in engagement prior to the separation thereof. In this respect the arrangement is as described in the Ainsworth Patent No. 1,762,604. The lifting rod is connected with suitable switch operating mechanism, not shown, arranged preferably mainly within the casing in such manner as to minimize possibility oi! gas leakage. The switch casing contains the gaseous arc extinguishing medium under substantial pressure above the atmosphere.

Fig. 1 is a set of experimentally-obtained curves illustrating the time of duration of alternating-' current sixty-cycle arcs, measured in cycles, for various arc currents and for the gases, air, nitrogen and helium. It will be noted that the arc duration in helium is much shorter, for any are current, than in either air or nitrogen and that, for currents above one thousand amperes, the time of duration of arc current is less than one cycle for helium while it is about five times as great (or air and nitrogen. It will also be noted that for higher arc currents, upwards of two thousand amperes, the arc is extinguished in helium in about one-half a cycle, which is as fast as is desired as a more rapid extinction may set up serious surges in certain circuits. On the other hand, for the same are currents, neither air nor nitrogen approach half cycle extinction.

The pressure or the medium, above a certain value, has no appreciable efiect on the time of arc duration. Fig. 2 is a set 0! curves showing the relation between time of arc duration and pressure, for helium and nitrogen. It will be noted that a pressure variation from sixty to one hundred eighty pounds gage resulted in practically no reduction in the time of arc duration. This is true also of air and other gaseous arc extinguishing media. The figure also illustrates the marked superiority of helium over nitrogen as an arc extinguishing medium.

In addition to its superiority over other media, helium has been found to be inert to the action of the arc. Air oxidizes the switch contacts. Nitrogen unites with any moisture present to form an acid which attacks the switch parts. Carbon dioxide is decomposed with deleterious results. Hydrogen combines readily with various substances and is combustible with air.

I claim:

1. In the art of rapidly interrupting high-voltage high-power alternating current circuits in which relatively movable solid contact members are disengaged for interrupting the circuit, the method of breaking the circuit which comprises drawing a heavy current arc by disengaging said contact members, and rapidly extinguishing said are in less than one cycle of arc current by subjecting said are to an atmosphere of helium at upwards of four atmospheres pressure.

2. In the art of rapidly interrupting high-voltage high-power alternating current circuits carrying upwards oi. five hundred amperes by disengaging relatively movable solid contact members, the method of interrupting the circuit which comprises drawing an are by disengaging said solid contact members, and extinguishing the arc in less than one cycle of arc current by subjecting said are to an atmosphere of helium at upwards of four atmospheres pressure.

3. In the art of rapidly interrupting high-vo1tage high-power alternating current circuits in which relatively movable solid contact members are disengaged for interrupting the circuit, the method of interrupting the circuit which comprises drawing a power are by disengaging said contact members, and subjecting said are to a rapid-arc-extinguishing atmosphere of helium at upwards of four atmospheres.

4. An electric circuit interrupter for high-power high-voltage electric circuits carrying upwards of five hundred amperes, said interrupter comprising relatively movable solid contact members between which an arc is drawn when said members are separated, and means for extinguishing said are in less than one cycle of arc current comprising an atmosphere oi. helium at upwards of four atmospheres pressure in which the arc is drawn.

WILLIAM S. EDSALL. 

